Push-pull rheostat



May 2, 1950 PUSH-PULL RHEOSTAT Filed Dec. 18, 1948 z- 2 mm H M""fimmmmuunz 54 FIG. 3 50 48 H. w. BATCHELLER iNVENTOR HUGH W.BATCHELLER ATTYS Patented May 2, 1950 UNITED STATES PATENT OFFICEPUSH-PULL RHEOSTAT Hugh W. Batcheller, Newton Highlands, Mass,

assignor to Ark-Les Switch Corporation, Watel-town, Mass, a corporationof Massachusetts Application December 18, 1948, Serial No. 66,055

3 Claims.

This invention relates to rheostats of the pushpull type wherein acontact element is pushed or pulled along a coil of resistance wire toany desired position, the contact element and an end of the resistancecoil being connected to leads from an electric circuit, whereby anydesired number of turns of the resistance coil can be cut into or out ofthe circuit.

An object of the invention is to provide a rheostat which is simple andrugged in structure and which is made of parts which are easily andcheaply made and assembled. As hereinafter described in more detail, arheostat is provided in which a helical resistance coil is embedded andsecured in a slot which extends through an insulating housing memberwhich is a rectangular block about as thick as the diameter of the coil.To this block is attached a boxlike member of sheet metal or any othersuitable material, thus forming an enclosure in which a contact memberis movable in contact with successive turns of the coil, a portion ofeach turn being exposed through the slot in the insulating block.

For a more complete understanding of the invention reference may be hadto the following description thereof and to the drawing of which:

Figure 1 is an exploded View of a rheostat embodying the invention;

Figure 2 is a plan view of the same;

Figure 3 is a section on the line 33 of Figure 2; and

Figure 4 is a section on the line 44 of Figure 2.

The rheostat illustrated in the drawing includes a housing comprising atop member or block It which is preferably of suitable refractorymaterial. This top member is of substantial thickness and is providedwith a central longitudinal slot 12 extending through the member fromtop to bottom. This slot is of sufficient width to receive a helicalcoil I A of resistance wire, the diameter of this coil beingsubstantially equal to the width of the slot, the length of the coilbeing substantially equal to the length of the slot. The walls of theslot converge slightly toward each other near the bottom thereof, asindicated at [6 in Figure 4. Thus, when the coil i 4 is inserted in theslot l2, it does not fall through but is caught by the converging lowerportions of the side walls. In order to maintain the coil permanently inplace, a layer of refractory cement 20 is applied to each of the sidewalls of the slot. The portions of the turns of the coil I4 which bearagainst the side walls of the slot are embedded in the cement 20, thelatter gripping the coil firmly when it hardens. Since the cement isrestricted to the side walls of the slot, portions of the coil remainex-,T posed at the top of the member 15 and also at the bottom of theslot I2. Before the coil 14 is inserted in the slot 12 in the course ofassem bling the rheostat, an end thereof is secured to a terminal member22. As indicated in Figures 1 and 3, this member may conveniently bemade of a strip of metal such as copper or brass bent to a U shape. Oneleg of the U is punched and tapped to form a threaded hole 24 to receivea binding screw 26 by which the end of a wire can be attached to theterminal 22. The mid portion of the terminal 22 is provided with astruck-up strip 28 under which an end of the coil I4 is thrust. Thestruck-up element 28 is then pressed down to pinch the wire and thus tomake a good electric connection between the coil [4 and the terminal 22.The terminal and coil can then be inserted as a unit in the member H],the slot l2 being provided with an extension 30 of reduced width toaccommodate the screw 26 when the terminal is assembled with the blockIn as indicated in Figure 3.

The other member of the housing is a boxlike receptacle 40 of sheetmetal such as soft steel which is pressed into suitable shape as shownin Figure 1. The receptacle 40 is preferably provided with a number ofup-standing cars 42 adapted to be bent into recesses 44- in the sides ofthe block In so as to overlap shoulders 46 in the recesses 44. Theseears, when r thus bent, hold the housing members It! and 40 in assembledrelationship in which they enclose a chamber 48 which is ventilatedthrough the slot l2.

Slidable in this chamber is a contact member 50 which has an element 52arranged to engage the portion of the coil I4 exposed through the bottomof the slot [2. The element 52 is resiliently pressed against the coilI4 by any suitable means. For this purpose, the contact member 50 may bemade of spring metal such as brass and be bent into U shape, one leg ofwhich presses against the floor of the receptacle 40, which is oppositeto the bottom of the block, the other leg of the member 50 terminatingin the element 52 which is pressed against the coil I4. The contactmember 50 is attached to the end of a stem 54 which slides through abearing member 56 at One end of the receptacle 4!]. The end of the stem54 may conveniently be secured to the contact member 50 by peening areduced end moves from turn to turn of the coil. Since the The element52 thus element 52 and the terminal 22, are connected 7 in an electriccircuit, such movement results in cutting in or cutting out successiveturns of the coil 14, thus increasing or decreasing the electricalresistance in the circuit in the usual manner. In the rheostatillustrated on thedrawing, the bearing member 55 is grounded, theterminal 22 being adapted to be connected to the'charged wire of thecircuit.

I claim:

1 rheostat having a housing which includes a block of insulatingmaterial having: a longitudinally extending slot therethrou h, said slotbeing slightly narrowed at the bottom thereof, a helical coil ofresistance wire secured in said MB? d amete 9 said i ens u a lly equalto the width of the slot, said housing also including a conductingmember spacedbelow the bottom or ,said slot, acontact element sl-ida'biein said housing with a portion resiliently pressing against the portionof the coil exposed through the bottom ofsaid slot and a portionpressing against said conducting member, and a terminal mounted on saidblock and electrically connectedto an end of said coil.

rheostat havin a housing which includes an elongated block 011insulating material having a longitudinal slot therethrough, said slotbeing slightly narrowed at the bottom thereof;,

said housing also including a box-like sheet metal member secured to theblock and forming a chamber therewith, a helical coil of resistance wiresecured in said slot, said coil having a length and diametersubstantially equal to the length and width respectively of said slot, acontact member slidable in said chamber in simultaneous contactv withthe portion of the 'coil exposed through the bottom of said slot andwith said sheet metal housing member, an operating -stern attached tosaid contact member and projecting out through an end of said sheetmetal member, and a terminal on said block electrica-lly connected to anend of said coil.

3. In a rheo stat, an elongated block of refractory material having alongitudinally extending; slot therethrough from top to bottom, saidslot being slightly narrowed at its bottom, a helical coil of resistancewire in said slot, said coil having a diameter substantially equal tothe width of said slot whereby said coil seats against the side walls ofthe slot where it narrows at its bottom, a layer ofreiractory cement oneach side wall of said slot in which adjacent portions of the turns ofsaidcoil are embedded to anchor the coil in the slot, and a terminalmembermountedon said block and electrically connect ed to an end ofsaid: resistanc wire.

nersaencns CITED The ollowin r ferences r o re ord the file of thisuatent: UNIT D $TATE llzEN'I Number Name Date 1,539,266 Mountford May'26, 1-925 1;, e2 ,23s Campbell Mar. 15," 192:2 2', 30e, 152 BatchellerDec; a2, 1942 2,420,807 Aufiero May 2 0', 1-94?

